Bur marigold / Amor seco (Bidens laevis)

Bidens is a genus in the daisy family Asteraceae. It contains about 200 species. The common names Bur marigolds or Tickseed sunflowers refer to the achene burrs on the seeds of this genus, most of which are barbed. The generic name refers the same fact; it means “two-tooth”, from Latin Bis “two” + Dens “tooth”. The plants are zoochorous; their seeds will stick to clothing, fur or feathers, and be carried to new habitat. This has enabled them to colonize a wide range, including many oceanic islands in South America. Bidens laevis is native from the southern half of the United States through Uruguay, where it grows in wetlands, including estuaries and riverbanks. This is an annual or perennial herb growing over 20 centimeters tall and sometimes much taller, exceeding one meter in height. The narrow lance-shaped leaves are 5 to 15 centimeters long, with finely toothed edges and pointed tips. The inflorescence bears one or more flower heads which bend down as they become heavy with fruit after flowering. Each head has a center of yellow disc florets and a fringe of 7 or 8 yellow ray florets each up to 3 centimeters long. The blooming period occurs from late summer to early fall and lasts about 1-2 months for a colony of plants. The root system is shallow and branches frequently. This plant often forms colonies and spreads by reseeding itself; sometimes the lower portion of a stem will form rootlets at the leaf nodes when it lies against moist soil.